This invention relates to the screening of an effluent having solid matter and the diversion of that solid matter to a grinding unit for purposes of size reduction. As is well known in waste water treatment, there are many environments where large volumes of liquid require initial processing for purposes of coarse screening so that large solid objects are diverted from the effluent stream and their size reduced by a grinding unit. The material, now of a reduced size, is either removed at the point of reduction or re-introduced into the stream for further processing downstream.
This invention is an improvement over the technology disclosed in U.S. Pat. No. 4,919,346. The '346 patent itself represented a significant improvement over prior vertically oriented belt screens which were typically used in waste water treatment plants for the purposes of removing solids from a liquid flow. Those prior devices thus utilized rakes, belts or the like which moved at an angle generally vertical, and therefore perpendicular to the fluid flow in a vertical plane. This resulted in undesirable hydrostatic effects in addition to a propensity of such systems to clog and require a considerable amount of power for purposes of lifting solid materials.
The '346 technology departed from this prior technique by placing a horizontally moving screen directly in the effluent flow with an adjacent macerator (grinder) disposed in that flow to receive solids that were diverted by the screen. Consequently, the screen allowed fluid to pass through it but at the same time presented a barrier for solid matter that could not pass through the screening elements. That solid matter was then diverted to one side of the effluent flow where it was then ground into smaller particles and then those particles placed back into the stream for substantive downstream processing.
A variant of the screening technique utilizing interleaved discs is disclosed in U.S. Pat. No. 5,061,380. The '380 also utilizes a solid grinder placed on one side of the screening unit.
A common deficiency with prior screening systems is that they were powered separately, using drive units separate from that of the grinding unit. In many installations the screen itself need not have that independent source of power. However, in the prior art the screening unit was considered to be a device separate from that of the grinding unit although, once installed they operated as a single system.
Another disadvantage in the prior art is that the placement of the grinding unit relative to the screening unit becomes critical for efficiency in the system. By having separate mounting frames, positioning and proper orientation became difficult to maintain across a matrix of different channel configurations. Prior systems employed internal deflectors inside the screen cylinder to use water flow for the purpose of removing debris from the screen surface and into the cutter. The internal deflector, while functional, added a degree of complication. Moreover, prior systems generally required the use of side rails on the cylinder side of the grinder. The use of the side rail tended to promote the passage of waste material through the grinder without clogging but is an expensive component to such systems.
Additionally, prior art systems tended to utilize screens mounted in separate frames adding additional elements and complicated geared/drive mechanisms.